1. Field of Invention
The present invention relates to biopsy needles which, under the guidance of medical imaging, are used to obtain tissue samples from lesions or drain fluid collections within the body.
2. Description of the Related Art
A frequent procedure in medicine is puncturing the skin with a needle and guiding the needle, using various imaging techniques, into a desired location within the body, typically for purposes of biopsy, fluid drainage, or catheter placement. In medicine, such a procedure is termed a percutaneous needle biopsy. With the advent of cross-sectional imaging techniques such as computed tomography, magnetic resonance imaging, and ultrasound, the use of these percutaneous image-guided procedures has increased dramatically.
Special needles, termed biopsy needles, are used for such procedures. These needles typically consist of a long, thin cylindrical tubular stainless steel shaft with a coaxial cylindrical bore, a central removable stylet (which occupies the bore when the needle is being placed into the body in order to prevent plugs of tissue from accumulating in and obstructing the bore), and an acute needle tip formed by a bevel imposed on the end of the shaft and accompanying stylet. Once the needle is in good position, the stylet is removed, thus exposing the bore of the needle to the target. This exposure allows a sample of tissue from the target to be obtained if the target is solid. If the target is a fluid collection, the fluid can be sampled and drained, if necessary.
Prior-art biopsy needles, as described above, are advanced into the target under direct visualization. However, when using such conventional needles, hitting the target during a procedure can be difficult if the target is small and/or deep within the body or if a direct linear path to the target is unavailable due to an obstructing object, such as a bone, vital organ, or major blood vessel.
When aiming for small, deep targets, even minor errors in the needle's initial direction can cause wide errors in needle tip position when the needle has reached the level of depth of the target. When this situation occurs, a significant length of the needle is withdrawn (typically) and the needle is then redirected and readvanced, hopefully providing a more accurate placement of the needle.
Lack of precise control of the needle during its placement is disadvantageous for several reasons. First, lack of precise control of the needle tip extends the time of the procedure. This is bad as gravely ill, very young or very old patients are typically unable to tolerate extended procedural times. Such patients are able to cooperate only to a limited extent with instructions such as lying flat, remaining motionless and holding the breath. Also, increased procedural times tie up the scanning machine, preventing the examination of other patients, thus indirectly increasing costs. Rates of complications increase both with extended procedural times and with multiple needle passes through the body. Common complications include bleeding (especially if the patient has a bleeding disorder or is on anticoagulant medication), collateral tissue damage, collapsed lung (in upper abdominal procedures), and pain. Increased doses of sedatives and narcotic analgesics may also be necessary for such extended procedures. Finally, some lesions are inaccessible using conventional biopsy needles as such lesions may only be accessible via nonlinear paths. Conventional biopsy needles are made to travel in linear trajectories.
The design of prior-art biopsy needles predate the advent of digital cross-sectional imaging. Not having the anatomic detail now available in modem imaging machines, steerable needles with precise control of the needle tip were not of interest; after all, if the anatomic details were unavailable, why would it be important to design a needle to avoid critical structures if those structures could not be visualized anyway. In fact, a design criterion for needles was that the needle travel in a straight path after introduction into the body. U.S. Pat. No. 2,830,587 (Everett, Apr. 15, 1958) describes various designs of needle shafts which are oval or elliptical in cross-section, the major axis of which is contained within an axial plane that also contains the tip. This arrangement causes the shaft to be more "resistant to bending" in this plane. With current imaging technologies, however, it is advantageous to have the needle travel along nonlinear paths such that critical structures are avoided and to have fine control over the needle tip so that small, deep lesions are more easily accessed.
Despite modern imaging technologies, reliance on conventional, prior-art biopsy needles in percutaneous interventional procedures with their attendant problems, as described above, continues.